Stock Rewards Vesting Inquiry

Apologies if this has been covered in a previous post, but did a search for some of the key words and wasn't finding anything that covered my specific case.

To cut right to it, I am an American citizen working for an American company in Japan.

I was awarded stock in our company as part of my bonus last year, and part if that reward will be vesting next month.

I am wondering what my tax obligations on this would be, and what the smartest "play" would be. From what I have been told from a co-worker is that this will count as income at the value at time of receiving the stocks (this makes sense). But that I will also have to pay tax on the additional income received when I sell (I believe he is referring to capital gains here). So he suggested to simply sell the moment I receive the stocks to only need to pay tax once, and then reinvest that income as I see fit. This to me however seems to be over complicating the situation. Why not just pay my tax on the income this year, and then hold till I am ready to retire and figure out the long term capital gains as I normally would?

Am I missing something here? Hoping someone can fill me in and make sure I am not shooting myself in the foot long term.

Thanks!

by sleepless_in_Osaka